 /*******************************************************************************
  * Copyright (c) 2005 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.internal.components.framework;

 import java.lang.ref.WeakReference ;

 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IConfigurationElement;
 import org.eclipse.core.runtime.IExecutableExtension;
 import org.eclipse.osgi.util.NLS;
 import org.eclipse.ui.internal.components.ComponentMessages;
 import org.eclipse.ui.internal.components.ComponentUtil;

 public class SingletonFactory extends ComponentFactory implements IExecutableExtension {

     private WeakReference singletonInstance;
     
     private ClassIdentifier classId = null;
     
     /**
      * Should only be called when this factory is created through an extension point.
      * If this constructor is used, the caller MUST call setInitializationData before
      * attempting to use the factory. Call one of the other constructors if instantiating
      * this object programmatically.
      */
     public SingletonFactory() {
     }
    
     /**
      * Creates a factory that creates instances of the given class
      *
      * @param classId name of the class to instantiate
      */
     public SingletonFactory(ClassIdentifier classId) {
         this.classId = classId;
     }
     
     /* (non-Javadoc)
      * @see org.eclipse.core.runtime.IExecutableExtension#setInitializationData(org.eclipse.core.runtime.IConfigurationElement, java.lang.String, java.lang.Object)
      */
     public void setInitializationData(IConfigurationElement config,
             String propertyName, Object data) throws CoreException {
     
         classId = ComponentUtil.getClassFromInitializationData(config, data);
     }
     
     public ComponentHandle createHandle(IServiceProvider availableServices)
             throws ComponentException {
         
         if (singletonInstance != null) {
             Object result = singletonInstance.get();
             if (result != null) {
                 return new NonDisposingHandle(result);
             }
             singletonInstance = null;
         }
         
         Class clazz = ComponentUtil.loadClass(classId);
         try {
             Object ref = clazz.newInstance();
             singletonInstance = new WeakReference (ref);
             return new NonDisposingHandle(ref);
         } catch (InstantiationException e) {
             throw new ComponentException(clazz, NLS.bind(ComponentMessages.Components_instantiationException, clazz.getName()), e);
         } catch (Exception e) {
             throw new ComponentException(clazz, e);
         }
     }

 }

